Many clinical situations benefit from regulation of the vascular, lymphatic or duct systems by restricting the flow of body fluid or secretions. For example, the technique of embolization involves the therapeutic introduction of particles into the circulation to occlude blood vessels. Permanent or temporary occlusion of blood vessels is desirable for managing various diseases, disorders and conditions. For example, permanent or temporary occlusion of blood vessels can be used to either arrest or prevent hemorrhaging or to cut off blood flow to a structure or organ.
Various polymer-based microspheres are currently employed to embolize blood vessels. These microspheres are usually introduced to the location of the intended embolization through microcatheters. Current commercially available embolic microspheres are composed of biostable polymers. Materials commonly used commercially for this purpose include polyvinyl alcohol (PVA), acetalized PVA (e.g., Contour SE™ embolic agent, Boston Scientific, Natick, Mass., USA) and crosslinked acrylic hydrogels (e.g., Embospheres®, Biosphere Medical, Rockland, Mass., USA). Similar devices have been used in chemoembolization to increase the residence time of a therapeutic agent after delivery. In one specific instance, a therapeutic agent (doxorubicin) has been directly added to hydrogel microspheres (prepared from N-acrylamidoacetaldehyde derivatized polyvinyl alcohol copolymerized with 2-acrylamido-2-methylpropane sulfonate) such that it can be released locally after delivery (e.g., DC Bead™ drug delivery chemoembolization system, Biocompatibles International plc, Farnham, Surrey, UK). Other examples of commercially available microspheres include glass microspheres with entrapped radioisotopes (e.g., 90Y), in particular, TheraSpheres™, MDS Nordion, Ottowa, Canada and polymer microspheres that contain monomers that are capable of chelating radioisotopes (90Y), in particular, SIR-Spheres®, SIRTex Medical, New South Wales, Australia.
It is also known to use polymer-based microspheres as augmentative materials for aesthetic improvement, including improvement of skin contour. Furthermore, polymer-based microspheres have also been used as augmentative materials in the treatment of various diseases, disorders and conditions, including urinary incontinence, vesicourethral reflux, fecal incontinence, intrinsic sphincter deficiency (ISD) and gastro-esophageal reflux disease. For instance, a common method for treating patients with urinary incontinence is via periurethral or transperineal injection of a bulking agent that contains polymer-based microspheres. The bulking agent is injected into a plurality of locations, assisted by visual aids, causing the urethral lining to coapt.